Automatic toner concentration control for use with crt input



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- GERALD L.WIEDERHOLD Nov. 5, 1968 M. H. oos'r ETAL 3,409,901

AUTOMATIC TONER CONCENTRATION CONTROL FOR USE WITH CRT INPUT Filed July 13, 1967 2 Sheets-Sheet 1 3 21 2 TONER FEED r SlGNAL MEANS OFF CRT SIGNAL I SOURCE 21 22 5 A TTORNE Y Nov. 5, 1968 M. H. DOST ETAL AUTOMATIC TONER CONCENTRATION CONTROL FOR USE WITH CRT INPUT Filed July 15, 1967 2 Sheets-Sheet 2 United States Patent O 3,409,901 i AUTOMATIC TONER CONCENTRATION CONTROL FOR USE WITH CRT INPUT Martin H. Dost, Los Gains, and Gerald L. Wiederhold, San Jose, Calif., assignors to International Business :Machines Corporation, Armonk, N.Y., a corporation of New York q .4 Filed ly.13, 1967, Ser. No. 653,140

' 7 Claims ..(Cl. 346-74 I ABSTRACT OF THE DISCLOSURE I In a xerographic system in which toner is used to develop latent electrostatic images generated bymeans of a.catho de-ray tube, a. toner concentration control system in which-toner is, fed to the developing mechanism in proportion to the area and density of print. The beam current of the CRT is integrated and when the total, which is proportional to the print density and area, exceeds a threshold, a batch of toner is released to'the developer mechanism and the integrator is reset. The predetermined level may be made variable such that when the toner level in the feed box is high, the threshold which must be exceeded is relatively high, while if the toner level is low the threshold which must -be exceeded is relatively low.

BACKGROUND OF THE INVENTION I I Field of theinvention This invention pertains to xerographic systems in general and more particularly to a system for automatically controlling the replenishment of toner to a development. mechanism. i v i w Description the prior art.-

Variations in toner densitymakeup have been found to be a major source of output variations in electrophotographic systems, both of the electrofax and xero. graphic types. In the past, several different methods of replenishing a toner supply have been employed. The-most, widely used method is a manual onein which the oper-. ator of the system views the output of the system and manually replenishes the toner when the legibility of the output falls below a subjective level. Other more sophisticated systemshave been employed. For instance, one such system which may be referred to as a feedback type systern utilizes a photocell scanner'to scan the, output and makesadjustments to the toner. supply whenever the image density falls below a-predetermined level.

The utilization of a manual system in whichthe operator continuously scans the output is, of course,.satisfactory in many applications. However, where a high throughput application exists, this type of manual control is highly unsatisfactory. Likewise, problems exist with the use of the currently available automatic toner control systems. For instance, it is. not only the variation in toner concentration which results in legibility variations in the output but in addition to the toner level variations, the original image density may varywand cause a legibility variation. In both ,the manual type system aswell as the photocell scanning system, this fact is not taken into consideration and adjustments to the system are made as if only the toner allects the output print. Ideally, adjustments to the toner supply in a developer mechanism should be made only if the output variations. in print density are caused by the absence of or an excess of toner in the developing mechanism.

SUMMARY Briefly, there is provided a feed forward toner control system as distinguished from a feedback toner control 3,409,901 Patented Nov. 5, 1968 See? system. A feedback toner control system is one in which the output print density is monitored and adjustments to the toner in the developing mechanism are made in accordance with the output print variations, whereas a feed forward toner supply or control is one in which corrections to the toner supply are made based onactual calculated toner usage. p

In the subject feed forward toner control system, the instantaneous beam intensity of a cathode .ray tube used for exposing the photoconductor is integrated, and when this integrated signal exceeds a threshold level a supply of toner is released to the associated developing mechanism. In a second embodiment, the threshold level is varied in accordance with the amount of toner contained in the toner supply bin such that with a large head of toner the threshold level is raised while conversely wit a small head of toner, threshold level is lowered.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a block-schematic drawing illustrative of the subject toner control system utilized in a xerographic mode;

In FIGURE 2 is shown a schematic of an integrator and threshold detect means which may be utilized as the toner feed signal means of FIGURE 1; and

FIGURE 3 is a schematic of a second embodiment of i the novel system wherein the threshold is made variabl in accordance with the toner head.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGURE 1 is shown a schematic of a commercially available CRT output printer. In FIGURE 1, a conventional xerographic drum 1 including a photoconductor on a conductive backing is shown mounted for rotation about axis 2. In FIGURE 1, as in the other figures, thesupports, bearings, drive mechanisms, etc., are not shown for purposes of simplicity. In FIGURE 1, a cathode ray tube 3 of conventional design has its light output beam 4imaged on the surface of the photoconductive drum 1. The photoconductive surface which was previously charged by means of a corona unit 5 is therefore selectively discharged by the light beam 4 to form a latent electrostatic image. The drum then is rotated past a developing station generally indicated at 6 at which toner 7 is cascaded merit. The developing mechanism 6 includes belts 8 with fingers 9 which pick up the toner 7 and carry it to the top of the belt and then dump it over the surface of the 'photoconductive drum 1 holding the latent electrostatic image. The toner supply 7, ask well known in the art, not only contains toner but additionally contains carrier beads to which the toner particles are triboelectrically attracted. As is well known, when the toner supply falls below a certain amount, the carrier beads which are cascaded over the surface of the photconductive drum 1 cease to deposit toner and instead often scrub toner which was previously deposited from the surface. This obviously results in poor image quality.

Following the developing station 6 the developed image is rotated into alignment with a transfer station generally designated 10 which includes a corona unit 11. The corona unit 11 deposits a charge on the rear surface of the paper web 12 to thereby pull toner from the photoconductive drum 1 onto the web. The web 12 then is moved through a fusing unit 13 wherein the toner is fused to the paper and the output web is taken as indicated by arrow 14. The drum 1 is then rotated past a cleaning station generally designated as 15 which includes a brush 16 which scrubs the drum clean of any residual toner.

The above described operation is well known; consequently, details of the corona units 11 and 5, the development mechanism 6, the fuser 13 and thecleaning station 15 will not be given. However, it should be understood that while the invention will be described in conjunction with a xerographic type process employing a developer as indicated at 6, that other types of developers such as a magnetic brush could be employed. For instance, the magnetic brush shown and described in U .S.P. 2,890,968 to Giamo, entitled Process and Developer Composition Therefor could be utilized in the subject system. Likewise, while a. xerographic type system is shown, the subject toner control system, as will be obvious to those skilled in the art, could be utilized in an electrofax process wherein the photoconductor is also the output medium.

As shown in FIGURE 1, the CRT 3 is driven by means of a CRT signal source which is connected along lines 21 and 22 to the grid of the CRT 3. The CRT signal source 20 may constitute any number of sources. For instance, the signal source may be taken directly from a computer or may be the output of a flying spot scanner or any other type of document scanner. The intensity signal 'from the CRT signal source which appears on lines 21 and 22 to the CRT 3 is also fed along line 24 to a toner feed signal means 25. The toner feed signal means 25 also receives an on/off signal along line 26 from theCRT signal sourceflhe output of the toner feed signal means 25 is applied along line 27 to the toner feed actuator 28 which is mechanically connected as illustrated by the dotted line 29 to the toner hopper generally designated at 30. There are numerous ways of releasing the toner 31 from the toner hopper 30 under control of the toner actuator 28. One such way is the widely used grate mechanism which will be described in more detail in conjunction with FIGURE 3.

In operation, the intensity signal from the CRT signal source 20 is fed along lines 21 and 22 and used to modulate the CRT beam intensity as the raster is swept over the face of the tube. The intensity signal 1 is also applied along line 24 to the toner feed signal means 25. The toner feed signal means 25 will have been actuated at the start of the print operation signal along line 26. The intensity signal appearing on line 24 from the CRT signal source is summed in the toner feed signal means 25 and when the summation exceeds a predetermined level, the toner feed signal means provides an output signal level on line 27 to the toner feed actuator 28 which causes the hopper 30 to release a predetermined amount of toner 31 into the developer mechanism 6. When the toner feed signal is supplied to line 27, the toner feed signal means is reset such that another summation process can take place. In this manner toner is released to the developing mechanism 6 in an amount proportional to the total area printed.

In FIGURE 2 is shown an integrator for summing the instantaneous beam intensity applied to the cathode ray tube and a threshold detector which detects the level of the integral (integral amount) and generates the toner feed actuator pulse and a reset pulse.

As shown in FIGURE 2, the on/off signal from the CRT signal source is applied along line 26 to a relay driver 35 which provides a drive pulse along line 36 to the relay coil 37 which causes the normally open relay arm 38 to come into contact with the fixed contact 39. This activates the toner feed signal means. The beam intensity signal from the CRT signal source which, as previously described in conjunction with FIGURE 1, is applied to the grid of the CRT 3 is also applied along line 24 through resistor 40 and stored in capacitor 41. Resistor 40 and capacitor 41 determine the time constant of the integrator. The charge on capacitor 41 builds up as the pulses from the CRT signal source are applied to line 24. Junction 42, which is connected to one side of capacitor 41 is also connected along line 43 to fixed contact 44. Relay 45, of which fixed contact 44 is a part, is normally open, as will later be described. Thus, the charge on capacitor 41 will continue to build up. Capacitor 41 will hold its charge for a long period of time due to the use of the insulated gate field efiect transistor 50. The output from the field effect transistor is applied along line 51 to the base of transistor 52. The combined operation of capacitor 41 and field effect transistor 50 to elfect efficient storage of the charge on capacitor 41 is described in more detail in the IBM Technical Disclosure Bulletin, volume 8, No. 6, 1965 at page 912.

When the charge on capacitor 41 exceeds arcertain level as reflected by a level rise on line 51,. transistor 52 will turn on. Transistor 52 is one transistor ofa conventional flip-flop pair, the other of which is transistor 53. Transistor 52 will be otf until the level appearing on line 51 applied through resistor 70 exceeds a pre-selected level. During the time that transistor 52 is oif, transistor 53 is on since a positive level is applied'to it through resistors 71 and 72. When transistor 53 is on, its collector and line 57 will be at near ground potential. When transistor 52 comes on, transistor 53 will go offsince the potential applied through resistor 72 to its base from the collector of transistor 52 is near ground. At this time the potential appearing at the collector of transistor 53 willswitch from ground to a positive potential. That is, when transistor 52 is 011, the collector of transistor 53 will be at ground potential since it is conducting; whereas, when transistor 52 is on, the collector of transistor 53 will be at the positive collector voltage since it is turned off. The pulses appearing in the collector circuit of transistor 53 are fed along line 55 to lines 56 and 57. Line 56 is connected to a single shot 58 which tires on the leading edge of positive going pulses on line 57 and applies a pulse along line 59 to the relay driver 60 which causes the relay arm 61 to close thereby grounding capacitor 41 and resetting the integrator. This same positive going pulse from the collector of transistor 53 is applied along line 57 to a second single shot 62 which generates a pulse which is applied along line 27 to the toner feed actuator.

Refer next to FIGURE -3 wherein is shown a system highly similar to that shown in FIGURES l and 2 with the added feature that-means are provided for varying the level at-which the flip-flop triggers in accordance with the amount of toner contained in the toner supply box which supplies toner to the developing mechanism.

The system of FIGURE 3 is similar in all respects to the systems of FIGURES 1 and 2 with the exception that the aforementioned means for providing a variable threshold to the flip-flop in accordance with toner head is provided. Thus, as shown in FIGURE 3, the signal from the CRT signal source is applied to the cathode ray tube 103 and utilized to write on the xerogra'phic drum 101 which, as previously described, forms a latent electrostatic image. The latent electrostatic image is rotated past development mechanism 106, transfer corona unit 111 and the fusing unit 113. The drum is then rotated past the cleaning station 115 and past the corona chargin-g unit 105. The signal applied to the cathode ray tube 103 is as described in FIGURES 1 and 2 integrated through resistor and capacitor 141 and held by capacitor 141. The charge appearing on capacitor 141 appears at the output of insulated gate field efiecttransistor and thus appears at junction 199. Junction 199 is connected through resistor 196 to the negative bias potential as in the case of FIGURE 2 which biases transistor 152 off. In parallel with resistor 196 is a potentiometer resistance which is connected through junction 200 to the negative bias potential. A sliding arm 194 is adapted to move along potentiometer resistance 195. As arm 194 moves upward, a smaller amount of the negative bias potential is applied through it to the base of transistor 152 while conversely, as the arm 194 moves down a larger amount of the negative bias potential is applied to transistor 152. Thus, as the arm moves downward, the net effect is that the charge on capacitor 141 must be increased to cause transistor 152 to come on. Conversely, as arm 1 94 moves upward, less of the negative bias potential is applied to it and a smaller positive charge on capacitor 141 will result in the turning on of transistor 152.

Shown in FIGURE 3 is a toner supply box 1 30 which holds a head of toner H which may be fed to the developing mechanism 106. As shown in the exploded view, a sensing mechanism composed of a float 190, a rod 191 and a. pivot 192 is utilized to move link 193 which moves arm 194 up and down. As the toner head decreases and arm 191 pivots about point 192, arm 194 will be moved upward which will cause less of the negative bias potential to be applied to arm 194. Thus, as the toner supply decreases, a smaller positive charge on capacitor 141 will be required to provide a net switching voltage through resistor 170 to the base of transistor 152. The reason for this arrangement is that one of the well known problems associated with a grate (gravity) feed mechanism, such as is shown in FIGURE 3, is that when the toner head is high, movement of the grate will result in a relatively large amount of toner being released to the development mechanism, while when the toner head is small, movement of the grate will result in a relatively small amount of toner being released to the development mechanism. The above element compensates for varying toner heads such that when the toner level in the feed box is high, the threshold level, which must be exceeded, is raised, while if the toner level is low, the threshold level is lower. The net result is that when the toner level in the feed box 130 is high, the flip-flop will require a higher positive charge on capacitor 141 before it switches and thus will switch fewer times. The converse is likewise true.

As with FIGURES 1 and 2, the output of the transistor pair 152 and 153 is taken from the collector circuit of traansistor 153 along lines 155 and 157 and a pulse is generated in single shot 162 and applied along line 127 to the grate actuator 201. Grate actuator 201 may be a solenoid which drives the grate 202 associated with the toner feed box to accomplish feeding.

It will be appreciated by those skilled in the art that the subject toner control system which has been described in a dry toner system may likewise be utilized in 'a liquid toning system. Additionally, while, referring particularly to FIGURE 3, a grate type toner supply mechanism is described which provides varying amounts of toner depending upon the toner head, the toner supply mechanism such as the well known metering mechanism is available which will provide uniform amounts of toner for each actuation.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in the form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In a system wherein a cathode ray tube is utilized to form a latent electrostatic image on a photoconductor to which toner is subsequently applied by a developing mechanism, a toner control system for regulating the amount of toner supplied to the developing mechanism comprising:

a toner supply means operative to supply toner to said developing mechanism;

a toner supply actuator means operative to cause toner to be released from said toner supply means to said developing mechanism;

a toner feed signal means operative to supply an actuation signal to said toner supply actuator after a predetermined amount of energy from said cathode ray tube has impinged on said photoconductor.

2. The toner control system of claim 1 wherein said predetermined amount of energy is determined by measuring the beam current of said cathode ray tube.

3. The toner control system of claim 2 wherein said beam current is integrated in an integrator.

4. The toner control system of claim 3 wherein the integral amount in said integrator is monitored by a threshold detector which, after the integrator exceeds a predetermined amount generates said actuation signal.

5. The toner control system of claim 4 in which a charge corresponding to the integral amount is stored in a capacitor which is discharged by said threshold detector when an actuation pulse is generated.

6. The toner control system of claim 4 wherein the threshold of said threshold detector is variable in accordance with the amount of toner held by said toner supply means such that as the amount of toner in said toner supply means decreases the threshold level is lowered.

7. The toner control system of claim 6 wherein a charge proportional to the integral amount is stored in a capacitor which is discharged by said threshold detector upon the generation of an actuation pulse.

References Cited UNITED STATES PATENTS 2,777,745 1/1957 McNaney 346--74 2,890,968 6/1959 Giai-mo -1.7 XR 2,956,487 10/ 1960 Giaimo 951.7 3,348,522 10/1967 Donohue 118-637 XR PETER FELDMAN, Primary Examiner. 

